Flexible LED assemblies and LED light bulbs

ABSTRACT

LED assemblies and related LED light bulbs. An LED assembly has a flexible, transparent substrate, an LED chip on the first surface and electrically connected to two adjacent conductive sections, a first wavelength conversion layer, formed on the first surface to substantially cover the LED chip, and a second wavelength conversion layer formed on the second surface. The flexible, transparent substrate has first and second surfaces opposite to each other, and several conductive sections, which are separately formed on the first surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of TaiwanApplication Serial Number 102132806 filed on Sep. 11, 2013, which isincorporated by reference in its entirety.

BACKGROUND

The present disclosure relates generally to flexible light emittingdiode (LED) assemblies and their applications, more specifically to theLED assemblies suitable for omnidirectional light appliances.

LED has been used in different kinds of appliances in our life, such astraffic lights, car headlights, street lamps, computer indicators,flashlights, LCD backlight modules, and so on. LED chips as lightsources for appliances are produced by wafer manufacturing process inthe front end, and then undergo LED packaging in the back end to resultin LED assemblies or apparatuses.

LED packaging mainly provides mechanical, electrical, thermal, andoptical supports to LED chips. LED chips, which are kind ofsemiconductor products, are prone to performance degradation, or aging,if exposed for a long time in an atmosphere of humidity or chemical. Toisolate the LED chips from the unfriendly atmosphere, epoxy resins arecommonly used to cover and seal them. Heat dissipation and lightextraction should be also considered for LED packaging, such that LEDproducts could have long lifespan, high brightness and powerconservation. For example, the heat generated by an LED chip, if notwell dissipated, could deteriorate the LED chip, shorten its lifespan,and downgrade its reliability. Optical design, such as the way toextract and direct the light into a preferable angle or distribution,also plays an important role for LED packaging.

Design for packaged white LEDs is more complicated and needs furtherconsideration of color temperature, color rendering index, phosphor,etc. A white LED could be provided by using phosphor to convert aportion of the blue light from a blue LED chip into green/yellow light,such that the mixture of the lights is perceived as white light by humaneyes. Because human eyes are vulnerable to high-intensity blue light,the blue light from a blue LED chip in a white LED package should notemit outward directly without its intensity being attenuated byphosphor. In other words, the blue light should be kind of “sealed” or“capsulated” by phosphor inside a white LED package so as to preventblue light from leakage to human eyes.

SUMMARY

An LED assembly comprises a flexible, transparent substrate, an LED chipon the first surface and electrically connected to two adjacentconductive sections, a first wavelength conversion layer, formed on thefirst surface to substantially cover the LED chip, and a secondwavelength conversion layer formed on the second surface. The flexible,transparent substrate comprises first and second surfaces opposite toeach other, and several conductive sections, which are separately formedon the first surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present disclosureare described with reference to the following drawings. In the drawings,like reference numerals refer to like parts throughout the variousfigures unless otherwise specified. These drawings are not necessarilydrawn to scale. Likewise, the relative sizes of elements illustrated bythe drawings may differ from the relative sizes depicted.

The disclosure can be more fully understood by the subsequent detaileddescription and examples with references made to the accompanyingdrawings, wherein:

FIG. 1 shows an LED assembly according to an embodiment of thedisclosure;

FIG. 2 is a cross sectional view of the LED assembly along alongitudinal line;

FIGS. 3A and 3B show two opposite surfaces of the LED assembly in FIG.1;

FIG. 4 demonstrates an LED filament produced from cutting the LEDassembly in FIG. 1;

FIG. 5 demonstrates an LED light bulb with the LED filament in FIG. 4;

FIG. 6 is an LED light bulb disclosed in the disclosure; and

FIG. 7 demonstrates an LED bulb disclosed in the disclosure.

DETAILED DESCRIPTION

An LED assembly 100 according to an embodiment of the disclosure isdescribed in detail with reference to FIG. 1, which shows perspectiveand cross sectional views of the LED assembly 100. As shown in FIG. 1,the LED assembly 100 is flexible, and is capable of being curved to be atape on a reel. Depending on actual applications, the LED assembly 100could be cut into pieces with proper lengths, each capable of being alight source in a lighting apparatus such as a light bulb. The crosssectional views A, B and C are derived from different locations of theLED assembly 100 in FIG. 1.

The LED assembly 100 has a flexible, transparent substrate 106, whichis, in one embodiment, composed of a non-conductive material such asglass or resin. The transparent substrate 106 has surfaces 102 and 104opposite to each other, and facing the opposite directions respectivelyand sidewalls 120 and 124 on the surfaces 102 and 104. As demonstratedin FIG. 1, the transparent substrate 106 is a thin, longitudinal strip,having two opposite ends 114 and 116. In this specification,“transparent” means having the property of transmitting rays of light,and could refer to as transparent, translucent or semitransparent. Thebodies situated beyond or behind the transparent substrate 106 could bedistinctly or obscurely seen. Thickness of the transparent substrate106, or the distance between the surfaces 102 and 104, could be 150micrometer or less.

FIG. 2 is a cross sectional view of the LED assembly 100 along alongitudinal line passing through ends 114 and 116. FIGS. 3A and 3B showtwo opposite surfaces of the LED assembly 100.

On the surface 102 of the flexible, transparent substrate 106 hasconductive sections 105, which are formed by printing for example.Another method of forming the conductive sections 105 includes formingdesigned conductive patterns through masks, comprising steps of coatinga conductive film on the surface 102, and patterning the conductive filmby lithography and etching to form conductive patterns on the surface102, wherein the conductive sections 105 can be further divided intodifferent conductive sections 105. The conductive sections 105 could becomposed of transparent material, such as indium tin oxide (ITO) orsilver thin film, and the thickness of the thin film should be wellcontrolled to be transparent to the light emitted from the blue LEDchips 108.

The embodiment in FIGS. 1, 2, 3A and 3B has blue LED chips 108 on thesurface 102, each connecting between two adjacent conductive sections105. In one embodiment, a blue LED chip 108 might have only one singleLED cell, having a forward voltage of about 2 to 3 volts, and this kindof LED chip is referred to as a low-voltage LED chip hereinafter.Comparatively, a blue LED chip 108 in another embodiment might includeseveral LED cells connected in series, and is referred to as ahigh-voltage LED chip hereinafter, because the forward voltage of theLED chip could be as high as 12V, 24V, or 48V, much higher than that ofa low-voltage LED chip. In one embodiment, each LED cell in an LED chiphas a light-emitting layer, and the LED cell might be formed on anepitaxial or non-epitaxial substrate. More specifically, the LED cellswithout individual substrate in a high-voltage LED chip are electricallyconnected to each other on a common substrate by semiconductorprocesses.

According to some embodiments of the disclosure, on the surface 102 ofthe LED assembly 100 are not only blue LED chips 108 but also LED chips(not shown) that emit light different than blue. For example, the LEDassembly 100 could include red, green, and/or yellow LED chips to havelight mixture with a desired spectrum or an appropriate colortemperature. Some or all of the LED chips in the LED assembly 100,whether it is blue or not, could be correspondingly replaced by LEDpackages with one or more LED chips in some embodiments.

The blue LED chips 108 in FIGS. 1, 2 and 3A are positioned on thesurface 102 and arranged as a row along a longitudinal line connectingthe ends 114 and 116. The cathode and anode of one blue LED chip 108contact with two adjacent conductive sections 105 respectively, in sucha way that all the blue LED chips 108 are electrically connected inseries and perform as an LED with a forward voltage higher than that ofthe individual LED chip 108, where the forward voltage is the summationof the forward voltages of the individual blue LED chips 108. Thisdisclosure is not limited to, however. In some embodiments, the blue LEDchips 108 and any other kinds of LED chips on the surface 102 could beconnected in many different configurations, including series, parallel,and the combination thereof.

In one embodiment, solder paste joints are used to mount the blue LEDchips 108 on the conductive sections 105, with a flip chip technique, toprovide both electric interconnection and mechanical adhesion. Eventhough solder paste is opaque, the joints hardly block or diminish thelight emitted from the LED assembly 100 because they are tiny in sizeand could be ignored in view of the overall light intensity. In anotherembodiment, an anisotropic conductive film (ACF) is used to mount theblue LED chips 108 on the conductive sections 105. For example, theconductive sections 105 are first coated with an ACF, and the blue LEDchips 108 are then mounted on the conductive sections 105 through ACF,which provides adhesion and electric connection between the blue LEDchips and the conductive sections 105. Alternatively, eutectic alloy orsilver paste could be employed to mount the blue LED chips 108 on theconductive sections 105.

In one embodiment, each of the blue LED chips 108 is mounted on aportion of the surface 102 where no conductive sections 105 are formed,and interconnection means, such as bonding wires, are then formed toconnect the blue LED chips 108 to the conductive sections 105. Inpractice, material with excellent thermal conductivity but poor electricconductivity is employed first to adhere the blue LED chips 108 to thesurface 102 or the LED chips 108 are directly connected to the surface102, and then bonding wires are provided to electrically connect blueLED chips 108 and conductive sections 105.

Over the blue LED chips 108 in FIGS. 2 and 3A is a phosphor layer 110, awavelength conversion layer. The phosphor layer 110 comprises epoxy orplastic and wavelength conversion material dispersed therein, such asphosphor or dye powder, that is capable of being stimulated by somelight emitted from the blue LED chips (with a dominant wavelengthranging from 430 nm to 480 nm) to produce green or yellow light (with adominant wavelength ranging from 540 nm to 590 nm), so that the mixtureof the lights is perceived as white light by human eyes. FIG. 1 isillustrative to show the blue LED chips 108 is under the phosphor layer110, but in some embodiments the blue LED chips 108 could not be seenbecause of the phosphor in the phosphor layer 110. The phosphor layer110 could comprise thermosetting resin, thermoplastic resin, light-curedresin, acrylic resin, epoxy, or silicone, for example.

FIGS. 2 and 3A show that the blue LED chips 108 are covered by thephosphor layer 110, which does not cover all conductive sections 105.The cross sectional view C in FIG. 1 also demonstrates a portion of aconductive section 105 is not covered by the phosphor layer 110. Thephosphor layer 110 shown in FIGS. 2 and 3A could form segments withdifferent sizes, and the segments are arranged in a row aligned with alongitudinal line connecting ends 114 and 116. The gap between twoadjacent segments exposes a portion of a conductive section 105.

Dispensing or screen printing could form the phosphor layer 110 on theblue LED chips 108. Each segment of the phosphor layer 110 could coverone or more blue LED chips 108. Possibly, one segment of the phosphorlayer only covers one blue LED chip 108, while another segment coversseveral blue LED chips 108. The phosphor layer 110 could be epoxy orsilicone, for example, dispersed therein with one kind or several kindsof phosphor, and the phosphor includes, but is not limited to, yttriumaluminum garnet (YAG), terbium aluminum garnet (TAG), Eu-activatedalkaline earth silicate, and SiAlON. The phosphor could begreen-emitting or yellow-emitting phosphor having elements selected froma group consisting of Sr, Ga, S, P, Si, O, Gd, Ce, Lu, Ba, Ca, N, Eu, Y,Cd, Zn, Se, and Al.

Thickness and coverage of the phosphor layer 110 could determine theflexibility of the LED assembly 100. The thicker the phosphor layer 110is, or the more the blue LED chips 108 that is covered by one segment ofthe phosphor layer 110, the less flexible the LED assembly 100 is.

As demonstrated in FIGS. 2 and 3B, on the surface 104, which is oppositeto the surface 102, is another wavelength conversion layer, the phosphorlayer 112, composition and manufacturing of which could be the same orsimilar with those of the phosphor layer 110. Similar with the phosphorlayer 110, the phosphor layer 112 is formed to have segments and gapsalternatively arranged in a row. Basically, segments of phosphor layer112 are formed on the positions of the surface 104 corresponding to theblue LED chips 108. Moreover, one segment of the phosphor layer 112 iscorresponding to one blue LED chip 108, to multiple blue LED chips 108,or to a segment of phosphor layer 110. In other words, each blue LEDchip 108 is substantially sandwiched by one segment of the phosphorlayer 112 and one segment of the phosphor layer 110. One segment of thephosphor layer 112, nevertheless, could be used for, in association withthe phosphor layer 110, sandwiching only one blue LED chip 108 in oneembodiment, or several blue LED chips 108 in another embodiment. Thephosphor layer 112 on the surface 104 might be absent in someembodiments while the phosphor layer 110 still presents. The phosphorlayer 112 and the phosphor layer 110 could differ in materials in thephosphor or in the lights emitted by the phosphors having same chemicalelements.

There on the surface 102 in one embodiment are red LED chips (notshown), and they could be sandwiched between the phosphor layers 110 and112. In one embodiment, covering on the red LED chips is not thephosphor layer 110, but a transparent resin or epoxy layer that has noor little phosphor; and there is no phosphor layer 112 on the locationsof the surface 104 corresponding to the red LED chips.

As demonstrated in FIG. 1, sidewalls 120 and 124 connect betweensurfaces 102 and 104, and are not covered or partially covered by thephosphor layer 110 or 112.

For assembling a lighting apparatus, a cutting instrument, such as apair of scissors, a slitter, a film slitter or a cutting machine, couldbe used to cut the LED assembly 100 at the locations where theconductive sections 105 located without being covered by the phosphorlayer 110 to result in several flexible LED filaments. An LED filament130 produced by the cutting is shown in FIG. 4, where the LED filament130 has, at its two ends, two conductive sections 105 uncovered by thephosphor layer 110 to be its cathode and anode respectively, from whichthe LED chips in the LED filament 130 might be driven by a power supply.

FIG. 5 demonstrates an LED light bulb 200 with the LED filament 130 inFIG. 4. The light bulb 200 further includes a bulb base 202, atransparent or semitransparent lamp cover 204, supports 206, conductivewires 207 and an LED filament 130. The bulb base 202 could be an Edisonscrew base capable of screwing into a matching socket and could beequipped with an LED driving circuit 208 therein. The lamp cover 204 isfixed on the bulb base 202, and the space enclosed by the lamp cover 204and the bulb base 202 is referred to as an inner space. Inside the innerspace, the LED filament 130 is fixed on the supports 206, which in oneembodiment are substantially transparent in regard to the light emittedfrom the LED filament 130. The LED filament 130 is curved to form acircle with a notch, and the circle is on a plane perpendicular to thescrew axis 212 of the bulb base 202 and the lamp cover 204. In otherwords, the screw axis 212 passes the center of the circle. Theconductive wires 207 could be used to mechanically support the LEDfilament 130. The conductive wires 207 also electrically connect the twoconductive sections 105 at two ends of the LED filament 130 electricallyand the LED driving circuit 208 in the bulb base 202, so that the LEDfilament 130 can be driven to illuminate.

Advantages of the LED assembly 100 are below.

1. Blue light leakage could be decreased or eliminated. The light thatthe blue LED chips 108 emit in all the directions confronts either thephosphor layer 112 or the phosphor layer 110, except the directions tothe sidewall 120 or 124. It implies that blue light leakage resultedfrom the blue light emitted from the blue LED chips leaves while thelight passing through the sidewalls 120 and 124. Experiment resultsdemonstrate that when the sidewalls 120 and 124 are small enough (or thesubstrate 106 is thin enough), for example smaller than 150 micrometerin height or in thickness, the blue light leakage through the sidewalls120 and 124 is hardly detectable and could be ignored.

2. Each blue LED chip 108 could light in all directions as it issubstantially not surrounded or encapsulated by opaque material. Thatis, the blue LED chip 108 is substantially surrounded or encapsulated bythe phosphor layers 112 and 110, two transparent layers with phosphordispersed therein.

3. The LED assembly 100 is easy for storage, as it could be curved intoa tape on a reel.

4. The length of an LED filament can be adjusted. For producing afilament with an expected length, it might only need a knife or a pairof scissors to cut at appropriate locations of the LED assembly 100.

5. The forward voltage of an LED filament can be adjusted. Based uponthe forward voltage required in an appliance, an assembler could cut theLED assembly 100 to have a filament with a suitable forward voltage. Forexample, if three blue LED chips 108 are connected in series betweenevery two adjacent exposed conductive sections 105 in FIG. 1, a filamentwith an integral multiple of three blue LED chips 108 connected inseries can be easily produced by cutting the LED assembly 100. In casethat there is only one blue LED chip 108 between every two adjacentexposed conductive sections 105, it is possible to form an LED filamenthaving any number of the blue LED chips 108 connected in series.

6. Simple assembling for a lighting apparatus. For example, theassembling could be realized by simple conventional soldering whichadjoins the conductive wires 207 and the LED filament. Supports 206 canbe optionally provided to support the filament 130 within the bulb atdifferent locations, and the power supply is connected to the conductivesections 105 at the ends of the filament 130.

7. Suitability for an omnidirectional lighting apparatus. As exemplifiedby the LED bulb 200 in FIG. 5, the filament 130 is curved to be almost acircle which is omnidirectional in respect with the screw axis 212,while the blue LED chips 108 in the filament 130 emit light in alldirections. Accordingly, the light bulb 200 could be an omnidirectionallighting apparatus while the lamp cover 204 is not opaque material.

Even though the filament 130 is almost in a shape of a circle in FIG. 5,the invention is not limited to. An LED filament according to thedisclosure is flexible and could be curved into any shape suitable for alighting apparatus. Another LED bulb 300 according to the disclosure isdemonstrated in FIG. 6, where the LED filament 130 has an arc, or acurved line shape, and is only supported or fixed in an inner space bytwo conductive supports. FIG. 7 demonstrates another LED bulb 400 of thedisclosure, which has a transparent or translucent serpentine tube 410,and the LED filament 130 meanders through its channel. Two exposedconductive sections 105 at the ends of the LED filament 130 in FIG. 7are soldered to conductive wires 404, which connect to a power supply(not shown) or a mains voltage plug (not shown) for supplying electricpower and illuminating the LED filament 130. In another embodiment, theLED filament 130 could be adopted as a lighting source within a channelletter.

As aforementioned, the LED assembly according to embodiments of thedisclosure is not limited to have only blue LED chips, and possibly hasLED chips with a color other than blue. Furthermore, and not all blueLED chips are covered by a common phosphor layer. In one embodiment ofthe disclosure, some blue LED chips 108 are covered by the phosphorlayer 110, but some are covered by another phosphor layer with phosphordifferent from that in the phosphor layer 110.

While the disclosure has been described by way of example and in termsof preferred embodiment, it is to be understood that the disclosure isnot limited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

What is claimed is:
 1. An LED assembly A light bulb comprising: aflexible, and transparent substrate, comprising: a first surface, asecond surface opposite to the first surface, and an end; an LED chip,which is flipped mounted on to the first surface; first and secondsurfaces opposite to each other; and several a first conductivesections, separately formed section and a second conductive sectionsuccessively formed on the first surface and separated from each other;an LED chip on the first surface and electrically connected to twoadjacent conductive sections; a first wavelength conversion layer,formed on the first surface to substantially cover flexible andtransparent substrate and directly contacting the LED chip, the firstconductive section, and the second conductive section; and a secondwavelength conversion layer formed on the second surface; and aconductive wire, formed on the first surface, extended beyond the end,and electrically connected to the LED chip, wherein, in a directionperpendicular to the first surface, the LED chip is overlapped with thefirst conductive section and the second conductive section, wherein thesecond conductive section has a wider portion and a narrower portion,and the wider portion is exposed from the first wavelength conversionlayer, and wherein the first conductive section has a uniform width, andthe second conductive section has a varying width.
 2. The LED assemblyas claimed in claim 1, wherein the transparent substrate is alongitudinal strip with two opposite ends, and the LED assemblycomprises LED chips arranged in a first row along a longitudinal lineconnecting the opposite ends.
 3. The LED assembly as claimed in claim 1,wherein the flexible, transparent substrate further comprises a sidewallconnecting the first and second surfaces, and at least a portion of thesidewall is not covered by the first wavelength conversion layer.
 4. TheLED assembly light bulb as claimed in claim 1, wherein the firstconductive sections are section is transparent in view of the to lightemitted from the LED chip.
 5. The LED assembly light bulb as claimed inclaim 1, wherein at least one of the conductive sections has a widerportion not covered by is exposed from the first second wavelengthconversion layer.
 6. The LED assembly as claimed in claim 1, wherein theLED chip is flipped over and mounted on the first surface.
 7. The LEDassembly light bulb as claimed in claim 1, wherein the first wavelengthconversion layer comprises a phosphor and the second wavelengthconversion layer are extended along a same direction.
 8. The LEDassembly light bulb as claimed in claim 1, wherein the LED assemblyflexible and transparent substrate is capable of being curved to be atape on a reel.
 9. An LED light bulb, The light bulb as claimed in claim1, further comprising: a base; and a lamp bulb, fixed on the base todefine an inner space; and wherein the LED assembly claimed in claim1chip is positioned inside the inner space and electrically connected tothe base.
 10. The LED light bulb as claimed in claim 9, wherein the LEDassembly is curved to have an arc.
 11. The LED light bulb as claimed inclaim 9 1, wherein the LED light bulb has a an imaginary screw axis andthe LED assembly flexible and transparent substrate is substantiallycurved to be on a an imaginary plane which is substantiallyperpendicular to the screw axis.
 12. The LED light bulb as claimed inclaim 11 1, wherein the LED assembly flexible and transparent substrateis capable of being curved to substantially be in a shape of a circle.13. The LED light bulb as claimed in claim 9, further comprising twoconductive wires respective connected to two of the conductive sections.14. The light bulb as claimed in claim 1, further comprising a supportsupporting the flexible and transparent substrate.
 15. The light bulb asclaimed in claim 14, wherein the support is not arranged on the end ofthe flexible and transparent substrate.
 16. The light bulb as claimed inclaim 14, wherein the support is substantially thinner than the flexibleand transparent substrate.
 17. The light bulb as claimed in claim 14,wherein the support has a portion substantially surrounding the flexibleand transparent substrate.